1. Field of the Invention
The present invention relates to a method for improving formability of a part made of advanced high strength steels and difficult to form, and more particularly, to a method for improving formability through a heat treatment and the like by irradiating a part made of advanced high strength steels and difficult to form with a laser.
2. Description of the Related Art
Recently, research interests in the steel industry and the automotive industry have been focused on improved strength and lightweight, and as the vehicle design has become complex and consumers' needs have been diversified, advanced high strength steels and the like having high strength and improved processability and formability are required. In particular, for advanced high strength steels used in vehicles, safety and the like accompanied by improved strength based on the trend have been considered to be important, and energy reduction accompanied by lightweight has also been considered to be important. In addition, as consumers' needs for design have been diversified and complex, a high-quality steel plate with sufficient formability is required, but advanced high strength steels in the related art have a limitation in being applied to parts which require complex forming due to low formability.
More specifically, the advanced high strength steels for a vehicle refers to a material having a tensile strength of about 590 MPa or more, is classified into dual phase steels composed of ferrite and bainite, TRIP steels composed of ferrite, bainite and residual austenite structures, and complex phase steels composed of complex structures of martensite, residual austenite, ferrite, bainite, and the like, and is selectively applied based on the purpose for each vehicle part. However, one of the greatest drawbacks of the advanced high strength steels is the limitation in being extensively applied to a part that may be difficult to form and the like due to low formability or a low elongation. Accordingly, there is a problem in applying the advanced high strength steels to vehicles.
Attempts have been made to improve formability of the advanced high strength steels using an induction heat treatment and the like, but since it is difficult to subject the advanced high strength steels to a local heat treatment, heat treatment is performed on the entire advanced high strength steels, and thus the overall strength may decrease due to an increase in formability of the advanced high strength steels.